I Can't Get No Less Diffraction ...

Started Mar 18, 2013 | Discussions thread
wfektar
Contributing MemberPosts: 690
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Re: Addendum: I Can't Get No Airy Action ...
In reply to Detail Man, Mar 18, 2013

Detail Man wrote:

<...>

While that was my original question, too, several sources seem to confirm this statement by Frans:

I lack the physics background to explain this properly, but it is squared because we are dealing with incoherent light, which is a safe assumption for typical photographic light sources. Coherent light sources, such as lasers, will have a sinc(x) diffraction pattern upon passing through a narrow slit.

http://mtfmapper.blogspot.com/2012/06/diffraction-and-box-filters.html

The sinc function is just the FT of a tophat. Don't muddy the waters with incoherent vs coherent.

... and thus it is the "intensity" (the square of the electromagnetic field strength in units of Volts/Meter, itself in units of Joules/Meter^2) seems to be what is used in these types of analyses.

We can't measure the field at optical frequencies -- it cycle averages to zero. We can measure the energy, which goes as the modulus square of the field, so that's where the square comes from.

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